This disclosure relates to a hybrid power plant system that incorporates a waste heat recovery system.
High fuel economy and low emissions are two design parameters for on-road vehicle power plants. A majority of passenger cars and light-duty trucks are powered with gasoline engines. For these vehicles, poor fuel economy is encountered during engine idling, such as during stops at traffic lights. Additionally, approximately 70%-90% of total hydrocarbon and carbon monoxide emissions occurred during the first two minutes after the engine has been started from a cold state. Subsequent to a cold start, the efficiency of a catalytic converter is low while the engine is operating in an open loop control state.
Forty-two volt hybrid systems have been proposed with an integrated starter/generator (ISG) to reduce engine idling conditions and recover some vehicle braking energy. With this type of hybrid system, the engine is shut off during stops, for example, while waiting at traffic lights. Thus, the overall fuel economy is significantly improved. Typically, some hybrid systems also incorporate a waste heat recovery (WHR) Rankin cycle to charge batteries by using waste heat from the engine to drive an alternator. Although such hybrid systems with waste heat recovery have done much to improve fuel economy and reduce emissions, there are opportunities for improvement.